In internal combustion engines including a plurality of cylinders and a fuel injector valve for each of the cylinders, for example, a multi-point fuel injection (MPI) engine with a fuel injector valve provided at an intake port of each cylinder, and an in-cylinder injection type internal combustion engine with a fuel injector valve for injecting fuel directly into a combustion chamber of each cylinder, an electronic control unit (ECU) operates to detect the start of cranking of the engine upon receipt of an ON signal from a cranking switch, and then to carry out cylinder identification based on signals received from a crank angle sensor and others. Once the cylinder identification is completed, the ECU drives the fuel injector valve of each cylinder with suitable timing so as to start the engine. In this operation, the ECU sets the driving period or duration of the fuel injector valve so that the amount of fuel ejected from the fuel injector valve during engine startup is larger than that ejected while the engine is idling after warm-up thereof. The amount of fuel ejected from the fuel injector valve during engine startup is relatively large for the reason as follows: where the engine is started in the cold state, and vaporization of the fuel injected into the cylinder is delayed due to a low temperature within the cylinder, for example, a sufficient amount of fuel required for combustion needs to be present around the spark plug so as to fire an air-fuel mixture without fail.
However, if the amount of the fuel is relatively large during startup of the engine as described above, the fuel injection amount per cylinder is increased, thus causing excessive racing of the engine upon combustion, or overshoot of the engine speed. Also, since the total amount of the fuel injected into the internal combustion engine as a whole is increased during startup of the engine, the fuel efficiency may be lowered, and exhaust gas characteristics may deteriorate due to increased unburned fuel components that were not used for combustion and that were eventually dispelled in exhaust gas.
As disclosed in laid-open Japanese Patent Publication No. 10-54272, for example where the water temperature is equal to or lower than a predetermined level after completion of cylinder identification, the fuel injection is halted for a period of time corresponding to two strokes, so that the temperature within the combustion chamber is increased due to a compression effect of the internal combustion engine, and the fuel injector valves are subsequently actuated.
The technique disclosed in the above publication, wherein the fuel injection is stopped for a period of two strokes after cylinder identification is completed, is advantageous in terms of the fuel efficiency and exhaust gas characteristics, as compared with the known technique of increasing the fuel amount. It is, however, difficult to achieve the desired temperature in the combustion chamber by utilizing the compression effect of the internal combustion engine, and the amount of the fuel injected after stopping the fuel injection for a period of two strokes must be determined taking account of the case where the temperature in the combustion chamber was not sufficiently increased, as in the known method of increasing the fuel amount. Also, since the fuel is injected into all of the cylinders in a specific sequence after a halt of the fuel injection, the total amount of fuel injection in the internal combustion chamber as a whole tends to be large during engine startup. Thus, there is a plenty of room for improvements in the above-described known methods, which are to be made for suppressing overshoot of the engine speed, and deterioration of exhaust gas characteristics and fuel efficiency.